LMH1251
YPBPR to RGBHV Converter and 2:1 Video Switch
General Description
Features
The LMH1251 is a wideband 2:1 analog video switch with an
integrated YPBPR to RGBHV converter. The device accepts
one set of YPBPR inputs and one set of RGB/HSYNC/
VSYNC inputs. Based on the input selected, the output will
be either a decoded TV or buffered PC video signal.
YPBPR to RGBHV conversion
YPBPR path: 70 MHz, −3 dB, 700 mVPP bandwidth
RGB path: 400 MHz, −3 dB, 700 mVPP bandwidth
Supports PC video display resolutions up to UXGA
(1600 x 1200 @ 75 Hz)
n Supports 480i, 480p, 576i, 576p, 720p, 1080i, and
1080p
n Smart video format detection for SD and HD
n Power save mode
The LMH1251 has a SYNC separator and processor that is
capable of extracting sync timing information from both Standard Definition Television (SDTV) and High Definition Television (HDTV) inputs. It provides bi-level sync, and tri-level
sync separation.
The color space conversion from YPBPR to RGB in the
LMH1251 is realized with a very high precision fully analog
dematrixer that provides chrominance accuracy that is less
than 2.5% of amplitude & 1.5˚ of phase error on a vectorscope. It is equipped with a smart video detection circuit
which automatically senses SDTV and HDTV video formats
and applies the appropriate color space conversion.
The LMH1251 is capable of handling SDTV, HDTV, XGA,
SXGA, and UXGA video formats, which makes it an ideal
solution for enhancing value in applications ranging from
LCD monitors, to set-top boxes, to projectors. The LMH1251
is part of the LMH™ high speed amplifier family and is
available in a TSSOP-24 package.
n
n
n
n
Applications
n
n
n
n
TFT LCD monitor
CRT monitor
Set-top box
Display projector
Connection Diagram
24-Pin TSSOP
20151927
Top View
© 2005 National Semiconductor Corporation
DS201519
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LMH1251 YPBPR to RGB Converter and 2:1 Video Switch
December 2005
LMH1251
Truth Table
TABLE 1. Input Select
Pin 24
OUT
0
RGBhv input Ch
1
YPBPR input Ch
TABLE 2. Format/Conversion Select
Pin 23
Pin 22
SYNC
Format Detection
0
0
Conversion Scheme
0
Bi-Level
Manual
480i/480p
1
Tri-Level
Manual
720p/1080i
1
*Outputs 0
Bi-Level
Auto
480i/480p
1
*Outputs 1
Tri-Level
Auto
720p/1080i
specify the format with Pin 22. With Manual Mode, Pin 22 is an input
pin. Since Pin 22 is a bi-directional pin, care must be taken to not apply
any voltages to it when it is in the Auto Mode, in which it functions as
an output pin. The use of the Auto Mode with Pin 22 left floating is
typically recommended.
Note: * When Pin 23 is set high, the LMH1251 is in Auto Mode, in which it can
detect the incoming video format (SD or HD) and apply the appropriate
color conversion and sync processing. With Auto Mode, Pin 22 becomes an output pin, and will either output a logic high or low to notify
the user of the format that is being detected by the LMH1251. If Pin 23
is set low, the LMH1251 is in Manual Mode, in which the user must
TABLE 3. Power Save
Pin 21
Low Power Mode
0
Disable
1
Enabled
Ordering Information
Package
24-Pin TSSOP
www.national.com
Part Number
LMH1251MT
LMH1251MTX
Package Marking
LMH1251MT
2
Transport Media
61 Units/Rail
2.5k Units Tape and Reel
NSC Drawing
MTC24
Thermal Resistance to Case
(θJC)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Junction Temperature (TJ)
400V
Supply Voltage VCC, Pins 7
and 17
5.5V
Voltage at any Input Pin (VIN)
−65˚C to +150˚C
Lead Temperature (soldering 10
sec.)
4.0 kV
Machine Model (Note 11)
+150˚C
Storage Temperature Range
ESD Tolerance
Susceptibility(Note 4)
25˚C/W
265˚C
Operating Ratings (Note 2)
Operating Temperature Range
VCC −0.5 ≥ VIN ≥ 0V
0.0V ≤ VIN ≤ 1.2V
Video Inputs (pk-pk)
Thermal Resistance to Ambient
(θJA)
0˚C to +70˚C
4.75V ≤ VCC ≤ 5.25V
Supply Voltage (VCC)
0.0V ≤ VIN ≤ 0.7V
RGB Video Inputs (pk-pk)
-0.3V ≤ VIN ≤ 0.7V
Y Video Inputs (incl. Sync)
110˚C/W
-0.35V ≤ VIN ≤ 0.35V
PBPR Video Inputs
Video Signal Electrical Characteristics
Unless otherwise noted: TA = 25˚C, VCC = +5.0V, RGB VideoIN = 0.7 VPP, Y VideoIN = 0.7 VPP, PBPR VideoIN = ± 350 mV,
CL = 8 pF, Video Outputs = 0.7 VPP. See (Note 7) for Min and Max parameters and (Note 6) for typicals.
Min
Typ
Max
Units
IS, RGB
Symbol
Supply Current
Parameter
No Output Loading, 80 kHz
Conditions (Note 2)
28
34
41
mA
IS, YPBPR
Supply Current
No Output Loading, 480p
see (Note 8)
60
70
80
mA
IS-PS
Supply Current, Power Save
Mode
Power Save Mode, No Output
Loading, 80 kHz, see (Note 8)
4
8
12
mA
1.8
2.1
2.4
VDC
IOUT
Output Current
VO BLK
Typical DC Active Video Black
Level Output Voltage
GainRGB
RGB Video Unity Gain
RGB VideoIN = 0.7 VPP
0.07
dB
Ch-Ch
MatchRGB
RGB Ch to Ch Matching
RGB VideoIN = 0.7 VPP
0.02
dB
LERGB
RGB Input: Linearity Error
Staircase Input Signal
see (Note 9)
0
%
1.55
ns
3
%
1.55
ns
3
%
1.54
ns
3
%
15.4
ns
3
%
15.4
ns
3
%
3
mA
Video Time Domain Response
RGB tr
RGB Input:
Video Rise Time
10% to 90%, AC Input Signal
(Note 5)
RGB OSR
RGB Input:
Rising Edge Overshoot
AC Input Signal
(Note 5)
RGB tf
RGB Input:
Video Fall Time
90% to 10%, AC Input Signal
(Note 5)
RGB OSF
RGB Input:
Rising Edge Overshoot
AC Input Signal
(Note 5)
SD YPBPR tr
SD YPBPR Input:
Video Rise Time
10% to 90%, AC Input Signal
(Note 5)
RGB OSF
RGB Input:
Falling Edge Overshoot
(Note 5), AC Input Signal
SD YPBPR tr
SD YPBPR Input:
Video Rise Time
10% to 90%, AC Input Signal
(Note 5)
SD YPBPR OSR
SD YPBPR Input:
Rising Edge Overshoot
AC Input Signal
(Note 5)
SD YPBPR tf
SD YPBPR:
Video Fall Time
90% to 10%, AC Input Signal
(Note 5)
SD YPBPR OSF
SD YPBPR:
Falling Edge Overshoot
AC Input Signal
(Note 5)
3
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LMH1251
Absolute Maximum Ratings (Notes 1, 3)
LMH1251
Video Signal Electrical Characteristics
(Continued)
Unless otherwise noted: TA = 25˚C, VCC = +5.0V, RGB VideoIN = 0.7 VPP, Y VideoIN = 0.7 VPP, PBPR VideoIN = ± 350 mV,
CL = 8 pF, Video Outputs = 0.7 VPP. See (Note 7) for Min and Max parameters and (Note 6) for typicals.
Symbol
Parameter
Conditions (Note 2)
HD YPBPR tr
HD YPBPR Input:
Video Rise Time
10% to 90%, AC Input Signal
(Note 5)
HD YPBPR OSR
HD YPBPR Input:
Rising Edge Overshoot
AC Input Signal
(Note 5)
HD YPBPR tf
HD YPBPR:
Video Fall Time
90% to 10%, AC Input Signal
(Note 5)
HD YPBPR OSF
HD YPBPR:
Falling Edge Overshoot
Min
Typ
Max
Units
8.4
ns
3
%
8.4
ns
AC Input Signal
(Note 5)
3
%
Video Frequency Domain Response
RGB BW
RGB Input:
Channel Bandwidth (−3 dB)
Large Signal BW
400
MHz
YPBPR BW
YPBPR Input (SD & HD):
Channel Bandwidth (−3 dB)
Large Signal BW
70
MHz
VSEP Ch-Ch
10 MHz
Video Amplifier 10 MHz Isolation
RGB Channel to Channel
(Note 12)
−50
dB
VSEP
Video Amplifier 10 MHz Isolation
RGB Input to YPBPR Input
(Note 12)
−55
dB
Signal to Noise Ratio
AC Input Signal, CL = 8 pF
(Note 12)
55
dB
INPUT-INPUT
10 MHz
SNR
Color Conversion Accuracy Unless otherwise noted: TA = 25˚C, VCC = +5.0V, Y VideoIN = 0.7 VPP,
PBPR VideoIN = ± 350 mV, CL = 8 pF, Video Outputs = 0.7 VPP. See (Note 7) for Min and Max parameters and (Note 6) for
typicals.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
VCOLOR ERROR
|PBPR| Amplitude
(Calculated from RGB Outputs)
YPBPR Video Input,
100% Color Bar (any 3 colors),
(Note 13)
± 0.3
± 2.5
%
θCOLOR ERROR
PBPR Phase Angle Calculated
from RGB Outputs)
YPBPR Video Input,
100% Color Bar (any 3 colors),
(Note 13)
± 0.2
± 1.5
deg
Max
Units
Sync Signal Electrical Characteristics
Unless otherwise noted: TA = 25˚C, VCC = +5.0V, Y VideoIN = 0.7 VPP, PBPR VideoIN = ± 350 mV, CL = 8 pF,
Video Outputs = 0.7 VPP. See (Note 7) for Min and Max parameters and (Note 6) for typicals.
Symbol
Parameter
Conditions
Min
Typ
VSYNCL
H & V SYNC Low Input
Pins 1 & 2
−0.5
1.5
V
VSYNCH
H & V SYNC High Input
Pins 1 & 2
3.0
VCC
+0.5
V
IO-SYNCH
H & V SYNC Current
Sink/Source Capability
5 kΩ Load
tR/F-SYNC
H & V SYNC Rise/Fall Time
tSYNC-WIDTH
H & V SYNC Width Error
Relative to H & V SYNC Input
H & V SYNC Input
tY-SYNC-WIDTH
H & V SYNC Width Error
Relative to Composite SYNCS
on Y
tSYNC-DELAY
50% of H & V SYNC Input to
Output
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3
mA
15
ns
5
%
Composite SYNC on Y Input
5
%
H & V SYNC Input
40
ns
4
LMH1251
Sync Signal Electrical Characteristics
(Continued)
Unless otherwise noted: TA = 25˚C, VCC = +5.0V, Y VideoIN = 0.7 VPP, PBPR VideoIN = ± 350 mV, CL = 8 pF,
Video Outputs = 0.7 VPP. See (Note 7) for Min and Max parameters and (Note 6) for typicals.
Symbol
Parameter
tY-HSYNC-DELAY
50% of H SYNC Input to Output
Conditions
Min
Composite SYNC on Y Input
(Not During Vertical Period)
Typ
Max
70
Units
ns
System Interface Signal Characteristics
Unless otherwise noted: TA = 25˚C, VCC = +5.0V, Y VideoIN = 0.7 VPP, PBPR VideoIN = ± 350 mV, CL = 8 pF,
Video Outputs = 0.7 VPP. See (Note 7) for Min and Max parameters and (Note 6) for typicals
Max
Units
VIL
Symbol
Logic Low Input Voltage
(Pins 24, 23, 22, 21)
Parameter
Conditions
−0.5
Min
Typ
1.5
V
VIH
Logic High Input Voltage
(Pins 24, 23, 22, 21)
3.0
VCC
+0.5
V
IL
Logic Low Input Current
(Pins 24, 23, 22, 21)
Input Voltage = 0.4V
± 10
µA
IH
Logic High Input Voltage
(Pins 24, 23, 22, 21)
Input Voltage = 0.4V
± 10
µA
VOL
Logic Low Output Voltage
(Pins 24, 23, 22, 21)
IO = 3 mA
0.5
V
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications, see the Electrical Characteristics tables.
Note 2: Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. All video inputs must be properly
terminated.
Note 3: All voltages are measured with respect to GND, unless otherwise specified.
Note 4: Human Body Model: 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Input from RGB signal generator: tr, tf = 1.5 ns. Input from SDTV YPBPR signal generator: tr, tf = 15 ns. Input from HDTV YPBPR signal generator: tr, tf = 8 ns.
Note 6: Typical specifications are specified at +25˚C and represent the most likely parametric norm.
Note 7: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. The guaranteed specifications apply only for the test conditions
listed. Some performance characteristics may change when the device is not operated under the listed test conditions.
Note 8: The supply current specified is the quiescent current for VCC and 5V with RL = ∞. Load resistors are not required and are not used in the test circuit;
therefore, all the supply current is used by the device.
Note 9: Linearity Error is the maximum variation in step height of a 16 step staircase input signal waveform with a 0.7 VPP level at the input. All 16 are steps equal,
with each at least 100 ns in duration.
Note 10: ∆AV track is a measure of the ability of any two amplifiers to track each other and quantifies the matching of the three gain stages. It is the difference in
gain change between any two amplifiers with the contrast set to AVC-50% and measured relative to the AV max condition. For example, at AV max the three
amplifiers’ gains might be 12.1 dB, 11.9 dB, and 11.8 dB and change to 2.2 dB, 1.9 dB and 1.7 dB respectively for contrast set to AVC-50%. This yields a typical gain
change of 10.0 dB with a tracking change of ± 0.2 dB.
Note 11: The Machine Model ESD test is covered by specification EIAJ IC-121-1981. A 200 pF cap is charged to the specific voltage, then discharged directly into
the IC with no external series resistor (resistance of discharge path must be under 50Ω).
Note 12: Measure output levels of the other two undriven amplifiers relative to the driven amplifier to determine channel separation. Terminate the undriven amplifier
inputs to simulate generator loading. Repeat test at fIN = 10 MHz for VSEP 10 MHz.
Note 13: Any three color bar signals can be used as test signals. The RGB outputs shall be used to calculate the amplitudes and phases of the chrominance results.
These should fall within the limits specified.
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LMH1251
Typical Performance Characteristics Unless otherwise noted: TA = 25˚C, VCC = +5.0V, RGB
VideoIN = 0.7 VPP, Y VideoIN = 0.7 VPP, PBPR VideoIN = ± 350 mV, CL = 8 pF, Video Outputs = 0.7 VPP. See (Note 7) for Min
and Max parameters and (Note 6) for typicals.
Large Signal Frequency Response
Crosstalk vs. Frequency
20151903
20151904
Pulse Response
Harmonic Distortion vs. Frequency
20151901
20151902
720p Color Bar Vectorscope
20151906
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6
GENERAL INFORMATION
The LMH1251 is a high-speed triple 2:1 video multiplexer
with an integrated sync processor and color space converter.
One input channel accepts standard RGBHV PC graphics
video and the second input channel accepts YPBPR component video. If the first input of the MUX is selected, the
device will output the RGBHV video from the input with unity
gain. If the second input of the MUX is selected, sync processing and color space conversion will be performed on the
YPBPR component signals to provide an equivalent RGBHV
signal at the output.
Note that in the AUTO mode, Pin 22 becomes an output pin,
and outputs a logic low if a SD video input is detected and a
logic high if a HD video input is detected, as notification to
the MCU.
MACROVISION COMPATIBILITY
The on-chip sync processor of the LMH1251 is fully compatible with DVD video sources which are embedded with Macrovision copyright protection. The LMH1251 will output Horizontal Sync pulses with consistent periodicity even during
the “Macrovision Sync” pulse period.
YPBPR to RGBHV PROCESSING
The LMH1251 is capable of processing 480i, 480p, 576i,
576p, 720p, 1080i, and 1080p/60 YPBPR component video
signals only. S-Video, composite NTSC, or composite PAL
video will not be converted by the LMH1251. For High Definition, 720p and 1080i/1080p video, the LMH1251 will convert the luminance and color difference signals into primary
RGB signals according to the linear arithmetic formula specified in the EIA/CEA-770.3-C Standard for High Definition
Analog Component TV. For Standard Definition video, the
LMH1251 will perform the conversion according to the linear
arithmetic formula specified in the EIA/CEA-770.2-C Standard for Standard Definition Analog Component TV. The
advanded analog architecture that is employed to perform
the color space conversion is precise to within 2.5% of
amplitude & 1.5˚ of phase error on a vectorscope with a color
bar test signal. This is illustrated with a vectorscope plot of a
converted color bar signal in the 720p format show in the
Typical Performance Characteristics section.
Note that although 480i/576i component video is supported
by the LMH1251, most PC Display Monitors cannot handle
such line rates. Typically, only 480p, 576p, 720p, and 1080i/
1080p are within the displayable line rate range of LCD and
CRT monitors. Furthermore, the scaler in LCD monitor systems must include a de-interlacer for it to display interlaced
video such as with 1080i.
POWER SAVE MODE
The LMH1251 is equipped with a power saving mode which
is controlled by Pin 21. This pin is a logic level input. The
device will enter a low power mode when the power save pin
is applied with a logic high by the MCU. Under these conditions, the IC reduces its current consumption to a minimum
as specified in the Electrical Characteristics section. However, the sync processor and switch will always remain
active. During power save mode, the RGB video outputs are
held to the blank level, while the sync signals are allowed to
continue to be processed and/or passed through. Based on
the absence or presence of sync signals at the output of the
LMH1251, the MCU can determine whether to bring the
system to a low power consumption state.
INTERNAL VOLTAGE REFERENCE
Proper operation of the LMH1251 requires a very accurate
reference voltage. This voltage is generated in the VREF
block. The output of the VREF stage goes to a number of
blocks in the video sections and sets the internal bias. To
insure an accurate voltage over temperature, an external
resistor is used to set the curent in the VREF stage. The
external resistor is connected to pin 15. This resistor should
be 1% and have a temperature coefficient under 100 ppm/
˚C.
Component Video Formats supported by the
LMH1251
480i
480p
OUTPUT DRIVE CHARACTERISTICS
The LMH1251 is designed to interface with an ADC or
preamplifier through an AC coupling capacitor as shown
below in Figure 1. The RGB outputs of the LMH1251 are 700
mVPP video signals with the black level at approximately 2V,
which is the chip’s internal voltage reference level. The H
Sync and V Sync outputs are CMOS logic outputs that swing
from 0 to 5V.
If the LMH1251 is to be designed into a stand-alone converter box application, the configuration in Figure 2 is recommended. The LMH6739, triple op amp with an internally
set gain of 2, can be used to drive RGB video over the VGA
cable out to a display monitor. Logic inverters are used for
driving the sync signals over the VGA cable.
576i
576p
720p
1080i23/25/30
1080p50/59/60
AUTO/MANUAL FORMAT DETECTION
The LMH1251 can either automatically detect the input format of the component video source, or it can be put in a
manual mode where the MCU has the flexibility to specify
which YPBPR to RGBHV processing scheme for the device
to apply depending on the input format. If a logic high is
applied to Pin 23, the LMH1251 will be in the AUTO detec-
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LMH1251
tion mode, which is typically recommended. In this mode, the
device will appropriately use the correct YPBPR to RGBHV
processing scheme based on its input format detection. If a
logic low is applied to Pin 23, the LMH1251 will be in the
Manual detection mode. In this mode, the MCU must apply a
logic low to Pin 22 if the processing scheme is for SD Video
formats, and a logic high if the processing scheme is for HD
Video formats.
Application Notes
LMH1251
Application Notes
(Continued)
20151908
FIGURE 1. Typical LMH1251 Application
20151907
FIGURE 2. Simplified Application Diagram for Driving a VGA Cable
LAYOUT CONSIDERATIONS
The most important point to note regarding the layout of the
LMH1251 on a PCB is that the trace length between the
output pins of the LMH1251 and the input AC coupling
capacitors of the next stage ADC or preamplifier must be as
minimal as possible. The trace lengths of the H Sync and V
Sync outputs should also be minimized, as the capacitive
loading on these outputs must not exceed 6 pF. For long
signal paths leading up to the input of the LMH1251, con-
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trolled impedance lines should be used, along with impedance matching elements. Bypass capacitors should be
placed as close as possible to the supply pins of the device.
The larger electrolytic bypass capacitor can be located farther from the device. The 10K external resistor should also
be placed as close as possible to the REXT pin. All Video
signals must be kept away from the REXT pin (15). This pin
has a very high input impedance and will pick up any high
frequency signals routed near it.
8
LMH1251
Test Circuit
20151928
FIGURE 3. Test Circuit
9
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LMH1251 YPBPR to RGB Converter and 2:1 Video Switch
Physical Dimensions
inches (millimeters)
unless otherwise noted
24-Pin TSSOP
NS Package Number MTC24
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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